The present invention relates generally to systems for switching optical signals and more particularly to optical switching devices used as components in such systems.
It is known to use mirrors in micro-machine devices to divert an optical signal from an input of the device to any one of a plurality of outputs of the device. For example, Lih Y. Lin describes such a device in the form of a Micro-Electro-Mechanical System (MEMs) in an article entitled xe2x80x9cFree-Space Micromachined Optical-Switching Technologies and Architecturesxe2x80x9d in OFC99 Session W14-1 Proceedings published Feb. 24, 1999. Optical signals switched by Lin""s device experience a power loss of about 5 dB when switched from an input to an output port of the device. While this amount of loss may be satisfactory for systems that switch optical signals through only one such MEMs switching device, the loss may be excessive for systems having multiple MEMs switching devices in a signal path. For example, a three-stage CLOS switching architecture of these MEMs switching devices in series would have a 15 dB power loss (i.e., 5 dB per stage) across the architecture from input to output.
In addition to power loss, another consideration in selecting an optical switching device is the ability to expand the input/output port capacity of an optical switching system built from the devices. This ability can be realized by providing each switching device with a plurality of input throughports, each input throughport aligned with a respective output port, and a plurality of output throughports, each output throughport aligned with a respective input port, as described in the related co-pending U.S. application Ser. No. 09/511,065. Expansion of the switching system can then be achieved by adding more MEMs switching devices to each switching matrix of the system and coupling output ports to input throughports and output throughports to input ports of adjacent MEM switching devices. This expansion can be realized without excessive losses since the maximum loss from port to throughport is significantly less than the maximum loss from port to port.
It may also be desirable to provide, in a switching matrix, the ability to add and drop optical signals from the matrix. For example, add/drop functionality is useful for performing wavelength conversion on signals switched by the system. Wavelength conversion is performed in order to alleviate blocking that occurs when two optical signals of the same wavelength need to egress a Wavelength Division Multiplexed (WDM) switching system from the same output port.
In view of the above, there is a need for an optical switching device that addresses the requirements of input/output port expansion and add/drop functionality described above. It would further be desirable that such a device be adequate for use in switching systems having multiple such devices in a switched signal path.
It is an object of the present invention to provide an improved optical switching device.
It is our intent to provide a switching element for use in a practical low cost wavelength plane switch. One aspect of this is a MEMS-based optical crosspoint array with six port groups (6P MEMS). Other aspects are providing optical amplification on a per optical wavelength controllable basis in the wavelength plane switch for both reducing/eliminating switch loss and for performing gain-flattening between paths through the switch in a commonly packaged module to control costs.
An embodiment of the present invention provides a single Hybrid Optical Integrated Circuit that contains the 6P MEMS, amplifiers, laser pumps (or inputs from laser pumps) in a single package. This is done either by providing alignment features between the MEMS devices and the amplifier silicon substrate, or by building both on a common silicon substrate.
According to an aspect of the present invention there is provided an optical switching device comprising:
a first optical switch matrix having first and second port groups associated therewith and a plurality of optical inputs and a plurality of optical outputs;
a second optical switch matrix having third and fourth port groups associated therewith and a plurality of outputs coupled to the plurality of optical input of the first optical matrix switch;
a third optical switch matrix having fifth and sixth port groups associated therewith and a plurality of optical inputs coupled to the plurality of optical outputs;
whereby the first optical switch matrix provides primary switching between the first and second port groups, the second optical switch matrix provides additional input port groups using the third and fourth port groups, and the third optical switch matrix provides additional output port groups using the fifth and sixth port groups.
According to another aspect of the present invention there is provided an optical switching device comprising:
a plurality of optical input ports;
a plurality of optical output ports;
a first matrix of optical divertors, each divertor being operable to divert an optical signal from one of the optical input ports to any one of a plurality of the optical output ports;
a plurality of optical expansion input ports, each one of the optical expansion input ports coupled to a respective optical output port;
a plurality of optical expansion output ports, each one of the optical expansion output ports coupled to a respective optical input port;
a plurality of optical inter-matrix input ports;
a second matrix of optical divertors, each divertor being operable to direct an optical signal from one of the optical inter-matrix input ports to any one of a plurality of the optical output ports;
a plurality of optical inter-matrix output ports; and
a third matrix of optical divertors, each divertor being operable to divert an optical signal from one of the optical input ports to any one of a plurality of the optical inter-matrix output ports.
The optical switching device provides the expansion capability and add/drop functionality desired via the optical expansion input and output ports and the optical inter-matrix input and output ports, respectively. Additionally, since these separate matrices of divertors are used to selectively couple the ports of the device, less divertors are required than if one large matrix of divertors were used. Further, the optical path length, a major issue in the design of such devices, is less in this structure than it would be in a single MEMS crosspoint providing a similar function.
Embodiments of the invention may include a plurality of optical amplifiers, each one of the optical amplifiers coupled in series with a respective optical output port or a respective optical inter-matrix output port.
The optical amplifiers compensate for the losses introduced into the optical switching path by the optical divertors on a path-by-path basis. This can be used to compensate for the loss of an individual switch stage or, for an externally introduced amplitude error such as that from a non-flat line system. Furthermore, the combination of amplification and switching can be used in multiple stage switches. This ability to compensate for signal power loss means the optical switching device can be used to build large switching matrices, for example 3-stage CLOS switching architectures.
Embodiments of the invention may be implemented as monolithic structures on a silicon wafer substrate. In this case optical amplifiers incorporated into an embodiment may take the form of an array of erbium doped Silica (Silicon Dioxide) or Phosphate-glass waveguides fabricated on a silicon or similar substrate, in combination with a an array of pump lasers, thereby enabling the gain of individual amplifiers to be set separately. First V-grooves in the silicon substrate provide alignment for rod lenses at inputs and outputs of the matrices of divertors and are sized to accept rod-lenses (which are large relative to the 6-10 xcexcm SiO2 waveguides) and to align the centers of these rod-lenses with the centers of the waveguides. The switching matrices are either fabricated directly on the silicon substrate or are fabricated separately and attached to the substrate after alignment with alignment feature, such as wells, etched in the substrate. Second V-grooves in the silicon substrate provide alignment for optical fibers that couple optical signals from the rod lenses or directly to the matrices of divertors. For example, these second V-grooves are dimensioned to align the core of a 125 xcexc fiber to the to the 6-10 xcexcm SiO2 waveguides. The facet angles in any V-groove are set by the crystal structure. Implementing the optical switching devices as monolithic structures on silicon wafers allows alignment features to be provided such that components of the devices can be positioned and interconnected within required tolerances.
Other aspects of the invention include combinations and subcombinations of the features described above other than the combinations described above.